1. Field of the Invention
The invention relates to Internet Protocol (IP) telephony and communication systems. Especially, the invention is related to such a system as specified in the preamble of the independent system claim.
2. Description of Related Art
At the time of writing this application, the trend in development of VOIP (Voice over IP) technology is towards integration of all communication technologies within workstations of users, i.e. using conventional personal computers as a terminal for voice and video communication as well as email and fax communication. One important development is the production of the Telephony Application Program Interface (TAPI) for personal computers, which allows developers to use a simple API (application program interface) for adding communication capabilities to their application programs. A typical configuration for a user workstation comprises an application program used for communication, such as for example an IP phone program or a video conferencing program, and a TAPI Service Provider (TSP) program for interfacing the application program to the VOIP network. The TSP program provides the TAPI which the application program uses, and communicates with the VOIP network elements according to H.323 standard and other related standards.
FIG. 1 illustrates a block diagram of an IP telephony system. FIG. 1 shows a VOIP network 50, comprising gatekeepers 51 for controlling connections within a part of the network and gateways 52 for connection of the network to other types of communication networks, for example. Typical VOIP networks utilize the H.323 standard. Such networks are well known for a man skilled in the art, wherefore the network elements of such networks and their functions are not elaborated here any further. FIG. 1 further shows a server unit 10 and a client unit 20. The client unit 20 comprises a TSP unit 12 and an application program 30, which is in this example an IP phone client program 30. The phone client program 30 communicates with the TSP program over the TAPI interface, transferring the call control (CC) information and audio information using the standardized calls of the TAPI interface. The server unit 10 comprises a TSP program for interfacing the server unit to the VOIP network 50, and an application server program 11 for controlling the application programs 30 of the clients 20, for which the server unit 10 is responsible. The application server program can be for example a control program for video-conferencing. The application server program 11 communicates with the TSP program 12 over the TAPI interface, transferring the call control (CC) information and audio information using the standardized calls of the TAPI interface. The application server program typically communicates directly with the client program 30 to control the functioning the client program and to provide such services to the client program, which cannot be realized using the TAPI interface. Typically, the interface A between the client program and the application server program is a proprietary interface of the maker of the application server program 11 and the client program 30.
In a typical installation a server unit 10 controls and provides services to a large number of client units 20. For the sake of clarity, FIG. 1 shows only one client unit 20.
However, this configuration has drawbacks. While the TSP program provides a standardized API for other programs such as the application server or the virtual phone to use, therefore making it easy to program such other programs and facilitating the use of programs from different manufacturers, the TSP program needs to be installed in each device used to access the VOIP network. This is a large drawback in large organizations, where the TSP needs to be installed to hundreds or even thousands of workstations.